Method for making lead frames for integrated circuit packages

ABSTRACT

Disclosed examples include a method of making a semiconductor die package comprising arranging at least one preformed die attach pad and at least two preformed leads on a lead frame carrier in a predetermined configuration to form a lead frame, attaching a semiconductor die to the at least one preformed die attach pad, wire bonding the semiconductor die to the at least two preformed leads, forming a molding structure including at least part of the semiconductor die and the at least two preformed leads, and removing the molding structure from the lead frame carrier.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of and claims priority to U.S.application Ser. No. 15/452,026 filed Mar. 7, 2017, now U.S. Pat. No.9,978,613 that issued May 22, 2018, the contents of which is hereinincorporated by reference.

BACKGROUND

Integrated circuit devices generally include an integrated circuit chipand a lead frame which are sealed within a protective enclosure, findwide use in various products, among which are consumer electronics,computers, automobiles, telecommunications and military applications.The lead frame electrically interconnects the integrated circuit chip tocircuitry external to the device. The lead frame is typically formedfrom a highly electrically and thermally conductive material, such ascopper or copper alloys. The lead frame material is stamped or etchedinto a plurality of leads, and a central area, called a die attach pad,onto which the integrated circuit chip is attached. The chip iselectrically connected to the leads, usually by wire bonding, and thedevice is encapsulated to provide mechanical and environmentalprotection.

Conventional lead frames for integrated circuit packages are typicallymade using metal etching processes to create die attach pads and leadsfrom a conductive layer of material on a bulk substrate or othermaterial. Such process involves etching the conductive layer of materialto form discrete conductor structures (e.g., the die attach pads and theleads). The etching process typically limits the spacing between the dieattach pads and/or between adjacent leads on these conventional leadframes to at least one thickness of the conductive layer of material dueto physical limitations of etching technology. In addition, the portionsof the conductive layer removed from the substrate during the etchingprocess generate waste in the manufacturing process. Manufacturer leadtimes for producing a new lead frame configuration via etching or otherprocesses also can be substantial.

SUMMARY

The present disclosure sets forth a method of making lead frames thatutilizes nearly all of the conductor material (incoming raw material forthe lead frame conductor structures) and produces lead frames withconductor structures (and/or other types of structures) having a spacingof less than one conductive layer thickness. The method of the presentdisclosure also affords rapid generation of new lead frameconfigurations without the need to retool and can result in reducedmanufacturer lead times. In one embodiment, preformed die attach padsand preformed leads are arranged on a lead frame carrier to form atleast one lead frame. A semiconductor die is then mounted to the dieattach pad, wire bonded to the leads, molded and singulated to produce asemiconductor package.

Disclosed example methods include singulating a plurality of conductivestructures from a sheet of conductive material, arranging the pluralityof singulated conductive structures on a lead frame carrier in apredetermined configuration, and arranging at least one die attach padon the lead frame carrier to form at least one lead frame having the atleast one die attach pad and a plurality of leads spaced apart from theat least one die attach pad. In one example, the conductive structuresinclude a first group of conductive structures having a first metalcomposition, size, shape or thickness and a second group of conductivestructures having a second metal composition, size, shape, or thickness,and the arranging the plurality of structures on a lead frame carrier ina predetermined configuration to form at least one lead frame includesusing at least one conductive structure from each group in the at leastone lead frame. The arranging the plurality of singulated conductivestructures on a lead frame carrier can include using a stencil, whereinthe stencil includes openings in locations corresponding to thepredetermined configuration, and wherein the stencil is applied over thelead frame carrier and the singulated conductive structures are placedon the lead frame carrier through the openings in the stencil. Inanother example, pick-and-piece machinery is used to arrange preformeddie attach pads and preformed leads on the lead frame carrier.

Another example method of making a semiconductor die package comprisesarranging at least one preformed die attach pad and at least twopreformed leads on a lead frame carrier in a predetermined configurationto form a lead frame, attaching a semiconductor die to the at least onepreformed die attach pad, wire bonding the semiconductor die to the atleast two preformed leads, forming a molding structure including atleast part of the semiconductor die and the at least two preformedleads, and removing the molding structure from the lead frame carrier.

Still another example method of making a semiconductor die packagecomprises singulating a plurality of conductive structures from one ormore sheets of conductive material, the conductive structures includingat least one die attach pad and at least one lead, arranging the atleast one die attach pad and at least one lead on a lead frame carrierin a predetermined configuration to form at least one lead frame,attaching a semiconductor die to the at least one die attach pad, wirebonding the semiconductor die to the at least one lead frame, applyingmolding over the semiconductor die and lead frame, and removing themolded semiconductor die and lead frame from the lead frame carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing an example method of fabricatingsemiconductor chip package according to one embodiment;

FIG. 2 is a perspective view of a plurality of die attach pads and leadssingulated from a sheet of material in accordance with the method ofFIG. 1;

FIG. 3 is a perspective view of an example lead and die attach padhaving a mold-lock feature formed during a singulation step of themethod of FIG. 1;

FIG. 4 is a flow diagram illustrating one example alternative forarranging preformed structures on a lead frame carrier in the arrangingstep of the method of FIG. 1;

FIG. 5 is a perspective view of the implementation of the example methodof FIG. 4;

FIG. 6 is a flow diagram illustrating another example alternative forarranging preformed structures on a lead frame carrier in the arrangingstep of FIG. 1;

FIG. 7 a perspective view of the implementation of the example method ofFIG. 6; and

FIG. 8 is a perspective view illustrating the singulation of a diepackage with lead frame from a molded strip of die packages inaccordance with the present disclosure.

DETAILED DESCRIPTION

In the drawings, like reference numerals refer to like elementsthroughout, and the various features are not necessarily drawn to scale.In the following discussion and in the claims, the terms “Including”,“includes”, “having”, “has”, “with”, or variants thereof are intended tobe inclusive in a manner similar to the term “comprising”, and thusshould be interpreted to mean “Including, but not limited to . . . ”Also, the term “couple” or “couples” is intended to include indirect ordirect electrical or mechanical connection or combinations thereof. Forexample, if a first device couples to or is coupled with a seconddevice, that connection may be through a direct electrical connection,or through an indirect electrical connection via one or more interveningdevices and connections.

Referring initially to FIG. 1, an example method 100 for making asemiconductor die package in accordance with the present disclosure isillustrated. The example semiconductor die package in the illustratedembodiment is a quad flat no-lead package (QFN package), but aspects ofthe present disclosure are applicable to other types of packages.

The method begins with process step 112, where a sheet of conductivematerial is obtained. The conductive material can be, for example,copper, aluminum, or any other suitable conductive material. In oneexample, the sheet of conductive material includes a copper layerpre-plated with NiPdAu. As will be appreciated, the sheet of materialcan be pre-plated with any desired plating material or plating stack ofmaterials to ensure proper bonding of components during downstreamprocessing. In addition, in process step 114 the sheet of material canoptionally be plated with various other conductive metals (e.g.,NiPdAu), for example, and/or roughened or undergo chemical surfacetreatment to enhance mold adhesion in later processing steps.

In process step 116, individual conductor structures are singulated fromthe sheet of material. The individual conductor structures can be, forexample, preformed die attach pads and/or preformed leads. Singulationof the individual structures can be performed in any suitable mannersuch as by sawing, etching, laser cutting, or other singulationprocesses. As will be appreciated, singulation of preformed die attachpads and/or leads from a sheet of material generally facilitates almost100% utilization of the sheet of material. Further, and as will bedescribed in more detail in connection with FIG. 3, the singulation stepor steps can be used to mill or otherwise create a mold-lock feature,such as a stepped edge or other profile, to enhance integration when thelead frame is molded over.

In process step 118, the singulated conductor structures are arranged orotherwise placed on a lead frame carrier in a predeterminedconfiguration to generate a plurality of lead frames. In thisdescription, a lead frame generally includes at least one die attach padand a plurality of leads arranged in proximity to the die attach pad. Ofcourse, aspects of the present disclosure can be used to make a varietyof structures in addition to lead frames, and the method of the presentdisclosure is, therefore, not limited to any particular lead frame (orother) structure.

As will be described in more detail below, positioning of the singulatedstructures can be performed in a number of ways, such as withpick-and-place machinery and/or through the use of stencils. It willfurther be appreciated that in one embodiment, the singulated structuresare secured to the lead frame carrier with an adhesive tape layer or thelike that maintains the singulated structures in position for subsequentprocessing steps. In addition, aspects of the present disclosure can beapplied to generate a wide range of lead frame configurations.

In process step 120, semiconductor dies are attached to the die attachpads of each lead frame in an otherwise conventional approach. Thesemiconductor dies are then wirebonded to the leads of each respectivelead frame in process step 122. A molding structure is then formed overat least portions of the dies, die pads, leads etc. in process step 124.After the molding structure is formed, the molding structure isseparated from the lead frame carrier and singulated (such as by sawing,for example) in process step 126 to generate individual semiconductorpackages.

Turning to FIG. 2, an example sheet of material 210 is illustrated. Thesheet 210 can be a sheet of conductive material such as copper or thelike. As noted above in connection with process step 114, the sheet 210can have various plating layers formed thereon and/or can be roughenedor otherwise processed (e.g., chemical surface treatment) to enhancemold adhesion in later processing steps. In accordance with process step116, the sheet 210 can be separated into a plurality of individualstructures, such as a plurality of leads 212 (individual leadsidentified by reference numeral 214) and/or a plurality of die attachpads 216 (individual die attach pads identified by reference numeral218). In some embodiments, the leads 214 and die attach pads 218 can bemade of a common material and/or singulated from a common sheet ofmaterial. In other embodiments, the leads 214 and die attach pads 218can be made of different materials and/or singulated from differentsheets of material. In either case, once singulated from a sheet ofmaterial, the individual structures in the illustrated example comprisepreformed die attach pads and/or preformed leads.

With reference to FIG. 3, it will be appreciated that certain mold-lockfeatures can be formed in the singulated structures during thesingulation process. In one embodiment, the mold-lock features caninclude a lead 314 or die attach pad 318 with one or more stepped edges316 and 320, respectively. The stepped edges provide additionalstructure and/or surface contour for integration of the preformed leadand/or die-attach pad with the molding structure. To this end, duringsingulation of the individual structures from the sheet(s) of material,extra material can be removed from the edge regions of the structuresbefore, during or after separation from the sheet of material. In oneembodiment, a trench is formed at least partially through the sheet ofmaterial and the individual structure is separated from the sheet ofmaterial in a location within the trench. This approach produces thestepped edge profile shown on the lead 314 and die 318 in FIG. 3. Otheredge shape profiles are also possible, such as beveled or dovetailed,for example. As noted above, regardless of the manner in which thepreformed leads and/or die attach pads are formed and/or otherwiseobtained, the structures are arranged on a lead frame carrier in apredetermined configuration to form lead frames, each having a dieattach pad and a plurality of leads spaced apart from the die attach padand each other.

Referring back to FIG. 1, and with further reference to FIGS. 4 and 5,process step 118 is the step wherein the singulated structures arearranged or otherwise placed on a lead frame carrier in a predeterminedconfiguration to generate a plurality of lead frames. FIG. 4 illustratesone example method 418 of carrying out process step 118 usingpick-and-place machinery for arranging the singulated structures on alead frame carrier.

Method 418 includes process steps 422 and 424 wherein a preformed dieattach pad is picked up and then placed on the lead frame carrier. Inprocess steps 426 and 428, a lead is picked up and placed on the leadframe carrier. The method 418 continues to decision box 430, whereat themethod reverts to process step 422 until the lead frame carrier iscomplete (e.g., all lead frames have been formed), at which time themethod 418 continues to process step 120 in FIG. 1. Thus, method 418 caninclude picking and placing multiple die attach pads on the lead framecarrier, and picking and placing a plurality of preformed leads inproximity to each die attach pad to thereby form a plurality of leadframes on the lead frame carrier.

In one example, each lead frame is assembled in full before the nextlead frame is assembled. In another example, several or all of the dieattach pads are picked and placed on the lead frame carrier and,subsequently, the preformed leads are then picked and placed inproximity to each die attach pad to complete each of the lead frames. Instill other examples, the preformed leads for some or all of the leadframes are picked and placed on the lead frame carrier and then the dieattach pads are picked and placed to complete the lead frames. Ofcourse, any suitable sequence of picking and placing the die attach padsand leads can be used.

FIG. 5 illustrates an example arrangement wherein a pick and-placemachine 510 is used to arrange the plurality of leads 212 and pluralityof die attach pads 216 in a predetermined configuration on lead framecarrier 514 to form a plurality of lead frames 518. It should beappreciated that a tape or other layer 522 is provided for temporarilysecuring the leads 214 and die attach pads 218 to the lead frame carrier514 after being positioned thereon.

Turning to FIGS. 6 and 7, another example method 618 for carrying outprocess step 118 of FIG. 1 is illustrated. In this method, two stencilsare used in succession for positioning the individual structures of eachlead frame on the lead frame substrate. Accordingly, in process step 622a first stencil is positioned on the lead frame carrier. In process step624, the preformed leads (or die attach pads, as the case may be) aredeposited onto the lead frame carrier through the openings in the firststencil.

In process step 626, a second stencil is positioned on the lead framecarrier. In process step 628, the preformed die attach pads (or leads,as the case may be) are deposited onto the lead frame carrier throughthe openings in the second stencil in the same manner as describedabove. Then, the method 618 reverts to process step 120 of FIG. 1.

FIG. 7 schematically illustrates an alternative embodiment of process618 where only one stencil 710 is illustrated. Stencil 710 includes aplurality of first openings 714 for receiving die attach pads 218 and aplurality of second openings 718 for receiving leads 214. It will beappreciated that the die attach pads 218 and leads 214 can be guidedinto the respective openings in the stencil or stencils using anysuitable method, such as vibration or the like, for example.

Turning to FIG. 8, the lead frame carrier 514 with a plurality of leadframes 518 is illustrated after process steps 120, 122, and 124 ofFIG. 1. As such, each lead frame 518 has a die 806 attached to itsrespective die attach pad 218 and wirebonded to leads 214. A moldingstructure 810 has been formed over the assemblies. As will beappreciated, the final step to forming a die package 816 is singulationof each die package from the molded strip of die packages. To this end,tape 522 is peeled off both the lead frame carrier 514 and the moldedstructure 810 thereby separating the molded structure 810 from thecarrier 514. The individual die packages are then singulated alongsingulation lines 832 into a plurality of individual die packages viasawing or any other suitable method.

It should be appreciated that aspects of the present disclosure not onlyfacilitate closer lead spacing than generally achievable using etchingor stamping processes, but can also facilitate producing lead frameshaving a relatively higher power capacity by allowing for the use of dieattach pads that are thicker than the leads. Thicker die attach pads canresult in improved thermal characteristics for a given lead frame. Otherlead frame construction approaches, for example etching approaches, havedie attach pads and leads of the same thickness. In addition, etchingprocesses have an upper limit to the thickness of the base material. Thepresent disclosure can be used to produce lead frames having die attachpads of a wider range of thicknesses and of thicknesses different fromthat of the leads. Moreover, and as previously noted, differentmaterials can be used for the die attach pads and the leads. All ofthese features result in a level of lead frame customization notgenerally available through prior approaches.

Aspects of the present disclosure are also well-suited to rapidproduction of new lead frame configurations. Unlike other approaches,the present disclosure does not require the production of any specialtooling for producing new lead frame configurations. It will beappreciated that current pick-and-place machinery can be used to producelead frames of a wide range of configurations without the need to firstgenerate special tooling, such as stamping or etching tools. Currentpick-and-place machine capabilities allow for placement at +/−10 micronsand ratios less than about 2%. Of course, aspects of the presentdisclosure are applicable to pick-and-place methods of any accuracy.Similarly, the stencils referred to above can generally be produced morequickly than other specialized tooling that would otherwise be used.This allows new configurations of lead frames to be produced much morequickly than some other approaches.

It should also be appreciated that aspects of the present disclosure arewell-suited to producing lead frames having a variety of configurationsincluding, but not limited to: a split die attach pad (lead frame withmultiple die attach pads and/or die attach pads of different respectivematerials), different base materials (lead frame with die attach pad ofa material different than the leads), thicker die pad (lead frame havinga die pad that is thicker than the leads), closely spaced leads (leadframe having leads with horizontal spacing less than one thickness oflead material), integrated passive components with smaller line/spacing(lead frame with passive components mounted adjacent chip on circuitboard), fused lead (lead frame with two or more leads fused together),chip on lead (lead frame with chip mounted directly on leads),dual/multiple rows of leads (lead frame having two or more rows ofleads, rows may have different heights or thicknesses), flip-chip onlead (lead frame having chip soldered to leads), non-conductive dieattach pad (PCB and/or substrate with embedded chip).

The above examples are merely illustrative of several possibleembodiments of various aspects of the present disclosure, whereinequivalent alterations and/or modifications will occur to others skilledin the art upon reading and understanding this specification and theannexed drawings. Modifications are possible in the describedembodiments, and other embodiments are possible, within the scope of theclaims.

The following is claimed:
 1. A method of making a leadframe comprising:singulating a plurality of conductor structures from a sheet ofconductive material; forming a plurality of leads by arranging theplurality of singulated conductor structures on a lead frame carrier ina predetermined configuration; and arranging at least one die attach padon the lead frame carrier to form at least one lead frame having the atleast one die attach pad and the plurality of leads spaced apart fromthe at least one die attach pad, the at least one die attach pad havingno protrusion of the conductive material from any corner.
 2. The methodof claim 1, wherein the arranging the plurality of singulated conductorstructures on a lead frame carrier includes using a pick-and-place robotto position individual conductor structures on the lead frame carrier.3. The method of claim 2, wherein the conductor structures include afirst group of conductor structures having a first metal composition,size, shape or thickness and a second group of conductor structureshaving a second metal composition, size, shape, or thickness, and thearranging the plurality of singulated conductor structures on a leadframe carrier in a predetermined configuration to form at least one leadframe includes using at least one conductor structure from each group inthe at least one lead frame.
 4. The method of claim 1, wherein thearranging the plurality of singulated conductor structures on a leadframe carrier includes using a stencil, wherein the stencil includesopenings in locations corresponding to the predetermined configuration,and wherein the stencil is applied over the lead frame carrier and thesingulated conductor structures are placed on the lead frame carrierthrough the openings in the stencil.
 5. The method of claim 4, whereinthe conductor structures include the at least one die attach pad and atleast one lead, the at least one die attach pad being larger than the atleast one lead, the method further comprising using a first stencil forarranging the at least one die pad on the lead frame carrier and,subsequently, using a second stencil for arranging the at least one leadon the lead frame carrier.
 6. The method of claim 1, further comprisingsecuring the conductor structures to the lead frame carrier with anadhesive tape interposed between the conductor structures and the leadframe carrier.
 7. The method of claim 1, wherein the singulating aplurality of conductor structures from a sheet of conductive materialincludes forming a mold-lock feature on the individual conductorstructures.
 8. The method of claim 7, wherein forming the mold-lockfeature includes forming a stepped edge formed by forming a trench inthe sheet of material having a first width, and severing the sheet ofmaterial at a position within the trench to generate the stepped edge.9. A method of making a semiconductor die package comprising: arrangingat least one preformed die attach pad and at least two preformed leadson a lead frame carrier in a predetermined configuration to form a leadframe, the at least one preformed die attach pad having no protrusionfrom any corner; attaching a semiconductor die to the at least onepreformed die attach pad; wire bonding the semiconductor die to the atleast two preformed leads; forming a molding structure including atleast part of the semiconductor die and the at least two preformedleads; removing the molding structure from the lead frame carrier. 10.The method of claim 9, wherein the preformed die attach pad includes aPCB.
 11. The method of claim 9, wherein the at least two preformed leadsinclude a first group of preformed leads in the form of conductorstructures having a first metal composition, size, shape or thickness,and a second group of preformed leads in the form of conductorstructures having a second metal composition, size, shape, or thickness,and wherein the arranging the at least two preformed leads on a leadframe carrier in a predetermined configuration to form a lead frameincludes using at least one conductor structure from each group in thelead frame.
 12. The method of claim 9, wherein the arranging at leastone preformed die attach pad and at least two preformed leads on a leadframe carrier in a predetermined configuration to form a lead frameincludes using a pick-and-place robot.
 13. The method of claim 9,wherein the arranging the at least one preformed die attach pad and atleast two preformed leads includes using a stencil, wherein the stencilincludes openings in locations corresponding to the predeterminedconfiguration, and wherein the stencil is applied over the lead framecarrier and the at least one preformed die attach pad and at least twopreformed leads are placed on the lead frame carrier through theopenings in the stencil.
 14. The method of claim 13, wherein the atleast one preformed die attach pad is larger in areal size than the atleast two preformed leads, the method further comprising using a firststencil for arranging the at least one preformed die attach pad on thelead frame carrier and, subsequently, using a second stencil to arrangethe at least two preformed leads on the lead frame carrier.
 15. Themethod of claim 9, further comprising securing the at least onepreformed die attach pad and at least two preformed leads to the leadframe carrier with an adhesive tape interposed therebetween.
 16. Themethod of claim 9, further comprising forming at least one of the atleast one preformed die attach pad and the at least two preformed leadsby singulating a conductor structure from a sheet of conductivematerial.
 17. The method of claim 9, further comprising wire bonding thesemiconductor die to the at least two preformed leads, applying moldingover at least a portion of the semiconductor die and lead frame, andremoving the molded semiconductor die and lead frame from the lead framecarrier.
 18. A method of making a semiconductor die package comprising:singulating a plurality of conductor structures from one or more sheetsof conductive material, the conductor structures including at least onedie attach pad and at least one lead, the at least one die attach padhaving no protrusion of the conductive material from any corner;arranging the at least one die attach pad and the at least one lead on alead frame carrier in a predetermined configuration to form at least onelead frame; wire bonding a semiconductor die associated with the dieattach pad to the at least one lead frame; applying molding over thesemiconductor die and at least one lead; and removing the moldedsemiconductor die and lead frame from the lead frame carrier.
 19. Themethod of claim 18, wherein the at least one die attach pad and at leastone lead are singulated from sheets of different materials, whereby theat least one lead frame has a die attach pad that is a differentmaterial than at least one lead.